Comments: ESP32 DevKitC V4

[utterances-bot]

ESP32 DevKitC V4 - DONE.LAND

Original DevKit from Espressif With Access to All ESP32 Pins – For Experienced Users

https://done.land/components/microcontroller/families/esp/esp32/developmentboards/esp32s/esp32devkitcv4/

[Tom-epd]

Hello, thank you for this detailled description of Devkitc v4. I have one of these boards equiped with a WROVER-IE ESP32 chip. It works very well when powered by USB, I try now to power it through a 3V3 regulated voltage, but doing this :

• The red power LED light up (with luminance lower than through USB)
• 2,8V can be measured on the 5V pin (seems that the LD1117 has no blocking diode)
• The ESP32 chip recieved a stable 3,3V on its power pin
• But the SW does not run (nothing happend)

Any idea why the SW does not run ?
thanks for your help
Best regards,
Tom.

[TobiasPSP]

There are many different vendors that produce a large range of variants. From what you describe, there must be 3.3v backfeeding. Still, the mcu dhould run, provided the external 3.3v supply is strong enough to be unaffected. Did you press Reset after uploading the firmware? I would measure the voltsge at 3.3v pin to ensure it is not dropping. And (if possible) I‘d check the trace to ensure that the 3.3v pin is indeed directly connected to the mcu. Let me know what you find. If time permits I‘ll repro on my side as well so we can compare findings.
After all, the mcu is running off the 3.3v, so the backfeed shouldn’t impact firmware execution.

[TobiasPSP]

The more I think about this, provided that your firmware runs fine with a 5v power supply and fails to run on 3.3v, I suspect that you either

• uploaded the firmware and then did not yet reset the chip -or-
• your 3.3v supply isn’t strong enough or has too much ripple (must be able to sustain 500mA spikes), causing brown outs and boot loop
  You may want to add a large capacitor (470uF+) to the 3.3v/gnd pin to smoothen the supply output, or use a lab bench power supply.

[Tom-epd]

Hello, Thank you for your answer. I have uploaded the firmware with the USB, and it runs without problem once connected to USB power supply. When I remove the USB, and plug my 3V3 power supply, it seems that SW isn't running anymore (no image update of my epaper device).
Currently, my power supply is a Texas Instrument bq25570 powered with a Lithium (currently 4,2V). I set-up some configuration resistor in order to deliver 3,38V. It seems to be stable with voltmeter, but I will check quality with a scope.
reading back the bq25570 datasheet, it seems that the ouput is limited to 100mA. So it could be the reason. I will try to add a large capacitor as you suggested.

[Tom-epd]

Indeed, the bq25570 does not deliver enough intensity :(
100uF is enough to make the module working great ! (but I will secure with more when I will activate WIFI)
Thanks alot for your help !

[TobiasPSP]

Awesome, I am glad this works for you!